Electronic structure calculations were performed using DFT and high-level ab initio methods to understandthe role of atomic halogens in the transformation of gaseous mercury in the Arctic atmosphere. The lattermethods were found to be superior in reproducing the reaction enthalpies as well as the geometrical parametersand vibrational frequencies, and therefore they were employed to calculate the energy potentials for the capture−deactivation approach to study the kinetics of halogen−mercury atomic recombination. Using the calculatedrate constants and inferred concentrations of halogen atoms in the Arctic troposphere, we found that atomicbromine might be responsible for the mercury depletion episodes.